Sound on film recording apparatus



y 1940- DEWAN SOUND ON FILM RECORDING APPARATUS Filed. Feb. 19, 1938 FIG. 3.

FIGZ.

INVEN TOR. LEON DEW/7N wmi j A TTORNEY,

Patented July 9, 1940 UNITED STATES PATENT OFFICE Leon Dewan, New York, N. Y., assignor of fifty per cent to George H. Gallaghan, New York,

. Claims.

This'application is in part a division of appli cations filed June 16, 1934, Serial No. 730.972 January 26, 1935, Serial No. 3,635. This app ication has matured into Patent No. 2,108,801.

The invention relates to improvements in sound recording and reproducing on film, and has for its object the recording of sound photographically by means of an incandescent filament in such a way that the high frequency compo- 1;} nents of the voice may be recorded upon the sound track of the usual 35 mm. films and also upon sound tracks of more slowly moving films such as the 16 mm. and even an 8 mm. size.

Another object of this invention is to produce a filament lamp for the purpose above mentioned that will be of microscopic dimension and still maintain a reasonably long life.

In this system variable electrical currents are Jnpressed upon a minute incandescent filament of platinum or tungsten or any desirable metal which is imaged upon a moving film. As the .zemperature of the filament varies in accordance ith the variable current, its effect upon the film aries accordingly} The filament is very minute and is in the form of a ribbon whose edge is presented toward the film. Its width and length may vary according to the size of sound track used and whether it is optically reduced or not but the thickness of the ribbon remains practically constant relative to the temperature employed as the speed of temperature responsive to the variable impressed current depends upon this dimension and the degree of the temperature of the filament. The filament is in ribbon form for the reason that a quick temperature response to impressed voice frequency currents is thereby attained. Were the ribbon of round cross section of the required diameter its mass would be too great to allow the speed of temperature response necessary.

In order to give the filament reasonably long life, an inert gas under one or more atmospheres of pressure is introduced within the lamp bulb. This high pressure retards volatilization and makes it possible to use the microscopic filament.

In imaging the filament upon the film it may be only slightly. reduced optically or not at all. Thus its length is kept small and the filament thereby rendered structurally firm despite its extreme thinness which is a constant quality, independent of any other dimensions which may be given to the filament in accordance with the optical arrangement used.

In the drawing:

Application February 19, 1938, Serial No. 191,363

Figure 1 is a diagrammatic view of a complete I recording system embodying this invention.

Figure 2 is a perspective view of the lamp and filament.

Figure 3 shows a circuit used for recording sound. I

Figure 4 shows diagrammatically a modified optical arrangement in connection with the invention.

In Figure 1, the filament l which is of ribbon form and whose fiat side is seen, is presented edgewise to the concave mirror 2 which images the edge only of the ribbon filament on the recording film 3.

The mirror which may be produced by a bright deposit of aluminum or silver upon a glass base to project a large percentage of the actinic rays, is spherical in form; and as shown by the dotted lines continuing its curve, the filament i andthe image on the film are at approximately the center of curvature of the mirror and as near as possible to its principal axis 4 4. As such a mirror is not only simple and inexpensive of construction but optical aberrations of any kind are avoided as a light wave originating in the plane at the centre of curvature tends to return thereto unchanged, and therefore the image formed on the film is sharp and clear.

The ribbon shaped recording filament which may range between 1 and 5 mils in width has a thickness which may range from of a mil to M mil. For example, with 16 mm. film sound track and no optical reduction of the filament, the filament may be only a little longer than the width of the sound track and may have a width of approximately 2 mil and a thickness of A; mil.

Since the speed of response depends upon the high temperature at which the filament is worked as well as the thinness, and since the life of the filament is reduced by an excess oieither of these factors, the thickness of the filament is made such that the necessary speed of response is attained at a temperature which does not greatly shorten the life of the lamp.

The presentation of the ribbon filament edgewise so that only its edge is imaged on the film regardless of the breadth of the filament, permits a fine scanning slit in combination with a strong filament.

As shown in Figures 1 and 2 the lamp is in the form of a small stout tube of glass which permits a large proportion of the actinic rays to emerge. Most of the interior of the tube is covered with a dull black deposit preferably of carbon paint so that no light except that of the filament itself shall leave the window and the image produced by the concave mirror shall be free of parasitic reflection effects.

The filament I is mounted between a stiff prong 5 and a thin flexible prong 6 which may be of phosphor bronze. The small rod "i is of a high resistance alloy and conducts a small part of the current between the electrodes 5 and G. This arrangement is for the purpose of compensating the efiect of temperature on the length of the filament I.

When the filament current is turned on, both the filament and the resistance rod I are energized, and while the rod I merely becomes warm and expands slightly it is nevertheless situated near the base of the prongs 5 and 6 so that its movement in expanding and separating the prongs is multiplied at the tips of the prongs where the filament I is mounted. The result is that the elongation of the filament when the current is turned on is compensated for by the efiect of the expansion of the rod I on the prongs 5 and I5. Furthermore due tothe fact that the prong 5 is thin and flexible, any inequa ty of the compensating eifect is taken up by the slight tension of the prong IS on the filament which is thus always maintained straight.

In Figure 3 showing the circuit used with this system of recording, the voice currents from the microphone 8 are passed through the amplifier 9 which is built to greatly favor the higher sound frequencies at the expense of the lower frequencies.

The output of the amplifier is fed to the step down transformer I II Whose secondary II is in series with the battery I2 and the filament I. The combined result of the voice currents in the secondary I I and the battery I2 is a sound varied direct current as the half cycles of the Voice currents in secondary I I alternately assist and oppose the steady direct current in battery I2.

A partial rectifier I3 across the secondary I I is caused to be adjustable in its effect and degree of rectification by means of the variable resistances I4 and I5. The purpose of this rectifier is to vary the temperature of the filament I in accordance with the volume of the sound to create what is known commonly as noiseless recording.

'For example if it is connected as shown, to block the battery current, then those half cycles in secondary I I which assist the battery and raise the filament temperature are partially shorted by the rectifier since the flow in its conductive direction, .while the half cycles which oppose the battery and allow the filament to cool are almost unaffected by the rectifier. Thus the cooling half cycles in secondary I I are favored at the expense of the heating half cycles, with the result that the mean filament temperature falls in proportion to the sound volume. This would produce a sound track on the film which could be played directly since it would be darkest at silence. If the rectifier I 3 is connected in the opposite direction across II it would produce a volume component bias in the usual manner wherein a positive print must 'be produced before reproduction is possible. The rectifier may be of the copper oxide type.

Figure 4 shows a modification wherein the image of filament I is optically reduced by a lens I6 and focussed on the film 3'. The ribbon filament is shown in cross section and the supports are eliminated for clarity of view. It will be seen that only the edge or thickness of the ribbon filament appears on the film and thus produces a fine scanning slit. To elucidate the nature of the arrangement, the lens I 6 may be likened to the lens of the eye and the film 3' to the retina of an observer. A filament presented as shown to the human eye in place of the lens and film would be seen only as a line of the thickness of the ribbon and the fiat sides would be invisible.

It is clear that this lamp and optical arrangement may be used for reproducing as well as recording sound.

Although the filament is here shown as transverse of the lamp proper, it is apparent that it can be placed at right angles to such position and present its edge through the end or top of the bulb.

What is claimed is:

In a second recorder or reproducer, means for producing an attenuated light bar, comprising means for producing the image of a ribbon shaped incandescent filament upon a film, the filament being presented edgewise to the image forming means.

2. In a sound recording system, a source of variable light comprising a minute incandescent filament upon which a fluctuating voice frequency electric current is impressed, said filament caused to be quickly responsive in temperature to the voice frequency electric fluctuations by having a cross section of two unequal dimensions, the larger dimension to provide structural strength and a smaller dimension for quick temperature response.

3. In a sound recording or reproducing system, a source of variable light comprising an incandescent filament having a cross sectional area of two unequal dimensions and upon which a fiuctuating electric current is impressed, said fluctuations being of voice frequencies, the filament being microscopic in at least one dimension of its cross section.

4. In a sound recording system, the combination of a film progressing mechanism, a lamp having a ribbon filament with one of its surfaces exposed to aifect the film for projecting light upon the film to produce a sound track, an amplifier of a type to favor the higher sound frequencies, a step-down transformer connected to the output of the amplifier, a battery connected to the secondary of the transformer and through the battery at one side to the lamp, whereby the combined result of voice current in the secondary of the transformer and the battery produces a sound varied direct current due to the half cycles of the voice current in the secondary of the transformer which assist and oppose the steady direct current from the battery.

5. In a sound recording system, as claimed in claim 4, wherein a rectifier is bridged across the terminals of the secondary of the transformer.

LEON DEWAN.

CERTIFICATE OF CORRECTION. Patent No; 2,206,88lp. I July 9, 191w.

LEON DENAN. It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows Page 2, second coIumn, line 214., 0191111, for the word "second" read -sound--; and

that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5rd day of September, A. D. 19m.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

